This invention relates to an apparatus for fastening a male screw such as a bolt or a female screw such as a nut to a mating female or male screw.
To fasten two mating screws together, it is necessary to first align accurately the center lines of the two screws and then to rotate one of the screws. The human hand is so skilful that it is capable of carrying out smoothly the screw fastening work. However the screw fastening work can not be said to be really suited for the human hand. On the assembly line of a given product, the screw fastening works of the same work pattern are sequentially repeated one after another. Sometimes large screws are employed. It is desired in such a condition to automatically execute the screw fastening work without relying upon the manual work.
It is actually difficult, however, to accurately align the center lines of two mating screws with each other without the manual work. One of preferred methods is to automatically correct non-alignment of the two center lines by the aid of a resilient mechanism even when both screws are not brought into accurate alignment with each other. Understandably, U.S. Pat. No. 4,098,001 is based upon this concept. The invention disclosed in this prior art employs such an arrangement that a rotational torque required for the screw fastening work is transmitted via bellows.
When large-sized screws are to be fastened, a stronger rotational torque is required for fastening them. Hence, it is a critical problem how to transmit the stronger rotational torque without sacrificing the function of the resilient mechanism.